Friday, April 11, 2008

Sun-climate link: a reply to Sloan and Wolfendale

Three weeks ago, we mentioned three recent preprints about cosmoclimatology, a theory in which galactic cosmic rays create clouds just like in a bubble chamber (and cool down the Earth unless they are filtered away).

Recall that the paper argued that the cosmic influence on the climate is probably insignificant because the effect seems to have a wrong "fingerprint" - i.e. the dependence on the latitude.

Second, the British critics argued that the cloud cover leads the cosmic ray flux variations by three months or so. As a bonus, the critics also question the correct behavior of the theory during the so-called Forbush events. We will mention this additional subtle "fingerprint", too.

Skeptics are familiar with both types of these arguments - fingerprints and lags - in a different context, namely in the context of the greenhouse effect. The greenhouse effect has a completely wrong fingerprint (see also Douglass, Christy, Pearson, Singer) and the historical CO2 concentrations lag behind the temperature by 800 years.

But seemingly similar arguments don't have to be equally valid. The main link of this article goes to Prof Nir Shaviv:

He explains that the fingerprint argument of the "skeptics" ;-) is incorrect because the cosmic rays relevant for cosmoclimatology are very high-energy (above 10 GeV or so), charged (ionizing) cosmic rays that are able to penetrate the atmosphere. These rays don't exhibit much variation caused by the Earth's magnetic field. It means that cosmoclimatology doesn't predict too strong a dependence on the magnetic latitude. It is only a few percent and the agreement was shown by Usoskin et al. (2004).

On the other hand, Sloan and Wolfendale incorrectly compare the cloud cover with the relatively low-energy cosmic rays that are absorbed in the upper layers of the atmosphere and that consequently have much stronger dependence on the latitude. These cosmic rays are almost exactly proportional to the flux of neutrons near the surface because the neutrons produced at higher layers of the atmosphere reach the surface almost without interruption. But they are also unable to ionize the atmosphere and create clouds.

Their failure to distinguish the different types of radiation - analogous to a naive skeptic's confusion between infrared and ultraviolet rays in the greenhouse effect - is the main reason for their faulty prediction of large latitude variations.

The lag

Another counter-argument by the "skeptics" :-) is the lag. Well, in this case, it is only argued to be around 3 months which is slightly less impressive a separation than those 800 years observed during the glaciation cycles, but 3 months is still a positive number.

This lag would indeed kill the causal relationship between cosmic rays and clouds if the cosmic rays were the only effect influencing the clouds. However, there are other effects, too. Only crazy people would like to argue that there only exists one cause of climate change and Nir Shaviv is not one of these crazy people.

Nir goes well beyond the handwaving above. In fact, he quantitatively estimates the lag and his prediction turns out to be compatible with observations. The essence of his calculation is simple. The cloud cover oscillations are assumed to have two components. One of them is a direct consequence of the cosmic rays, as dictated by cosmoclimatology. It has virtually no lag and induces changes of the cloud cover by roughly 1.5% (Nir shows that this follows from the sensitivity corresponding to 1 - 1.5 per CO2 doubling).

However, the other component of the cloud cover is dictated by temperature which is known from Shaviv (2005) to lag by 1/8 of the solar cycle behind the solar activity and it induces fluctuations of the cloud cover by roughly 0.17-0.35%, about 5-10 times smaller than the zero-lag component.

It follows that the lag of the mixture will be 1/8 times (1/5 or 1/10) of the cycle which is between 1.8 and 3.5 months, fitting Sloan & Wolfendale's figure beautifully. The lag has the opposite sign because the two components have the opposite signs from one another, too. The major component - direct cosmoclimatology - reduces clouds during the solar maxima while the subleading component adds clouds near the solar maximum through an increased temperature and increased evaporation. If you want a numerical model behind the idea, cos(x) - cos(x+1/8)/5 = a cos(x-1/(8*5)b) where a,b are numbers close to one. 1/8 should have been 2.pi/8 but you surely get the idea and you can refine the equation. ;-)

There is no paradox here.

Note that you can't use the same argument to get rid of the 800-year-lag problem of the greenhouse effect. What's the difference between the two situations? The difference is that in cosmoclimatology, both the temperature and the cloud cover depend on external (solar, cosmic) perturbations that are primary and the strongest ones and such an effect doesn't contradict any data.

On the other hand, the temperature in Al Gore's graphs is claimed to be driven by CO2 itself, not by external "third" effects, and such a hypothesis is falsified by the temperature-CO2 lag. The lag either means that a "third" external quantity independently drives both the temperature and the CO2 (that don't interact with each other much) - which seems unlikely - or that the temperature's effect on the carbon dioxide is stronger than the opposite (greenhouse) effect. The latter option is almost certainly correct and the mechanism behind this relationship is called outgassing.

Forbush events

Finally, Sloan & Wolfendale complain that one more fingerprint is not seen. During the so-called Forbush events when the cosmic ray flux drops by 15-20%, they don't observe a huge enough decrease of the cloud cover.

However, the Forbush decreases only last for a few days while the "skeptics" determine the cloud cover from the weekly and monthly average data. The average weekly or monthly decrease of the cosmic ray flux is much smaller even during weeks or months with the Forbush decreases - because the latter only take two or three days - and the corresponding weekly or monthly decrease of the cloud cover is actually small enough that it can't be isolated from the noise.

To do it right and to see some signal, one would have to consider daily averages of the cloud cover data. And indeed, it was done by Harrison and Stephenson (2006) who have apparently confirmed the drop of clouds over Britain.

After reading Nir Shaviv's answer in detail, I seem to have a very clear opinion who knows what he is talking about and who knows it a little bit less. ;-) Unfortunately, Terry Sloan who happens to be a member of the LHC's ATLAS collaboration belongs to the latter category.